Multi-layered silver halide grains are known, such as those described in JP-A-60-143331, JP-A-62-196644, JP-A-61-112142, etc. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) In JP-A-62-123445, disclosed are tabular, multi-layered silver halide grains having an aspect ratio, which is represented by the ratio of the circle-corresponding diameter of the major face of the grain to the thickness of the grain, of 1 or more. However, these are not high silver chloride grains such as those directed to by the present invention but are essentially silver iodobromide emulsions. In these prior art references, there is given no disclosure relating to silver chloride grains having (100) face as a major face.
The known, multi-layered silver iodobromide grains have high sensitivity and high resistance to pressure fog but have lower solubility than silver chloride grains. Therefore, though having high sensitivity, these are not applicable to photographic materials to be processed rapidly. This is because, when photographic materials having such silver iodobromide grains are processed, iodide ions and bromide ions are accumulated in the developer being used thereby lowering the activity of the developer and retarding the development of the materials. In addition, the fixation of silver iodobromide emulsions progresses slowly and therefore the emulsions are not applicable to rapid processing.
There are many references relating to tabular silver halide grains having a high silver chloride content. As references relating to tabular silver halide grains having (111) face as a major face, for example, mentioned are JP-B-64-8326, JP-B-64-8325, JP-B-64-8324 (the term "JP-B" as referred to herein means an "examined Japanese patent publication), JP-A-1-250943, JP-B-3-14328, JP-B-4-81782, JP-B-5-40298, JP-B-5-39459, JP-B-5-12696, JP-A-63-213836, JP-A-63-218938, JP-A-63-281149, and JP-A-62-218959.
As references relating to tabular silver halide grains having (100) face as a major face, mentioned are JP-A-5-204073 (corresponding to U.S. Pat. No. 5,292,632), JP-A-51-88017 (corresponding to U.S. Pat. No. 4,063,951), JP-A-63-24238 (corresponding to U.S. Pat. No. 4,777,125), etc.
However, there is no reference relating to multi-layered, high silver chloride grains having (100) face as a major face and having a high bromide layer inside of the grain.
It is known that, in the crystal of a silver chloride grain, (100) face has a more stable crystal habit than (111) face and the former is advantageous for adsorption of dye thereonto, etc. Therefore, it is easy to obtain silver chloride grains having high sensitivity. However, uniform silver chloride grains are often fogged when they are chemically sensitized. In addition, since silver chloride grains having a uniform structure in terms of halide composition are not specifically constructed in such a way that the charge separation of electrons and positive holes to be formed in the grains when the grains have absorbed light is accelerated, the formation of latent images in or on the grains is often inefficient.
Moreover, silver chloride grains having elevated sensitivity are easily fogged under pressure. Therefore, it has heretofore been impossible to realize silver chloride grains having elevated sensitivity and elevated resistance to pressure fog.
Since initial fixation of silver halide grains having an outermost layer having the largest Br content rate is retarded, such grains are not the most suitable for rapid fixation where the amount of the replenisher to the fixer being used is reduced.
In the present specification, "Br content rate" means a Br mol rate based on a silver halide composition constituting a region (layer) in a silver halide tabular grain. For example, the "Br content rate" is "y" when the silver halide composition in the region (layer) is AgI.sub.x Br.sub.y Cl.sub.z and x+y+z=1.
We, the present inventors have assiduously studied various types of silver halide grains having the same total silver halide content so as to realize silver halide grains having the highest fixability and having the highest resistance to fatigue of fixers and, as a result, have found that (100) major face-high silver chloride tabular grains having an inside region having the highest Br content rate are the best.
When such (100) major face-high silver chloride tabular grains having an inside region having the highest Br content rate are exposed to light, positive holes generated by the exposure are gathered in the inside region and are forcedly separated from electrons while the rebinding of the positive holes and the electrons is inhibited. Accordingly, the formation of latent images on the grains is enhanced. In particular, the formation of a latent images on the (100) face as a major face of the tabular grains is especially enhanced.
The existence of the high Br content rate region inside of the grain is equal to the introduction of the gap of halide composition and also the introduction of crystal defects (dislocation, etc.) into the inside of the same, and it is well known that the introduction of these has the effect to reduce pressure fog. We, the present inventors have also found, as a result of our assiduous studies, that high silver chloride tabular grains having a major face of (100) outstandingly exhibit this effect.